Hard disk drive having a damper for reducing vibrations

ABSTRACT

A hard disk drive having a vibration reducing damper is disclosed. The hard disk drive is provided with a damper which is interposed between a through hole provided at a cover plate and a screw joined to the upper end of the shaft of a spindle motor, and includes at least one viscoelastic material layer. It is preferable that the damper has a multi-layered structure in which at least one high stiffness layer has relatively higher stiffness and at least one low stiffness layer made of a viscoelastic material has relatively lower stiffness. With the above configuration, the damper restrains vibrations generated by the spindle from being transferred to the cover plate, noises generated by the hard disk drive are reduced, and, in addition, since vibrations generated by the spindle motor are damped, disk fluttering is reduced.

RELATED APPLICATION

This is a divisional of application Ser. No. 10/175,952 filed Jun. 21,2002. The entire disclosure of the prior application Ser. No. 10/175,952is considered part of the disclosure of the accompanying divisionalapplication and is hereby incorporated by reference.

The present Application claims priority from Korean Patent ApplicationNo. 2001-55557 filed on Sep. 10, 2001; the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hard disk drive, and moreparticularly, to a hard disk drive having a vibration-reducing damperbetween a spindle motor and a cover plate.

2. Description of the Related Art

A hard disk drive is one of the auxiliary memory systems of a computer,and is intended to read stored data from a stack of magnetic disks, orto write data to the magnetic disks with magnetic heads. Recently,various research and development have been performed in order to realizehigher speed, more increased storage capacity, and more reducedvibrations and noises of such a hard disk drive.

FIG. 1 is an exploded perspective view schematically illustrating aconventional hard disk drive, and FIG. 2 is a vertical section viewillustrating an assembly structure of a housing and a spindle motor ofthe hard disk drive shown in FIG. 1.

Referring to FIG. 1, a hard disk drive is provided with a housing 10, aspindle motor 30 installed in the housing 10 for rotating magnetic diskunit (hard disk unit) 20, and a head assembly 40 for reading data fromthe magnetic disk unit 20 or writing data to the magnetic disk unit 20.

The housing 10 is installed in a main body of a computer, and comprisesa base plate 11 for supporting the spindle motor 30 and the head stackassembly 40, and a cover plate 12 which is joined to the upper part ofthe base plate 11 for enveloping and protecting the magnetic disk unit20 and the like. The housing 10 is usually made of a stainless steel oraluminum alloy material.

The magnetic disk unit 20, a recording medium for writing data thereto,has one or a plurality of magnetic disks spaced a predetermined distancefrom each other, and is installed to be rotated by the spindle motor 30.

Now, an assembly structure of the housing 10, the spindle motor 30, andthe magnetic disk unit 20 will be described in detail with reference toFIG. 2.

The spindle motor 30 is supported by a flange 31 which is fixedlyinstalled on the base plate 11. The lower end portion of a shaft 32 ofthe spindle motor 30 is fixed to the flange 31, and the upper endportion thereof is directly fixed to the cover plate 12 by a screw 39.To this end, a through hole 13 is formed at the cover plate 12 so thatthe threaded portion of the screw can pass through the through hole 13.A hub 33 is installed on the outer circumference of the shaft 32 withbearings interposed therebetween so that the hub 33 can rotate. Themagnetic disk unit 20 is fixedly installed on the outer circumference ofthe hub 33. When the magnetic disk unit 20 has a plurality of magneticdisks, one or more ring-shaped spacers are installed on the outercircumference of the hub 33 to maintain a predetermined distance betweenthe disks. In addition, a clamp 35 is joined to the upper portion of thehub 33 to prevent the magnetic disk unit 20 from being separated fromthe hub 33.

As described above, the conventional hard disk drive has a structure inwhich the shaft 32 of the spindle motor 30 is directly joined and fixedto the cover plate 12. As a result, since vibrations generated by thespindle motor 30 are directly transferred to the cover plate 12, andagain transferred to the base plate 11 connected to the cover plate 12,there is a problem in which the whole hard disk drive vibrates, andaccordingly noises increase.

The vibrations generated by the spindle motor 30 are transferred to thecover plate 12 in the form of vibrations in the axial direction of theshaft 12 and rocking mode vibrations. Although, in order to block suchtransference of vibrations, there is a method in which the shaft 32 isnot joined to the cover plate 12, this results in another problem. Thatis to say, when the shaft 32 is not joined to the cover plate 12, therocking mode frequency of the spindle motor 30 becomes lower.

Accordingly, since the rocking mode frequency may match a vibrationfrequency of the spindle motor 30 due to allowable tolerance, assemblytolerance, and the like of a ball bearing of the spindle motor 30, thereis a possibility that the resonance phenomenon can severely affect theperformance of the hard disk drive. In addition, vibrations generated bythe spindle motor 30 result in fluttering of the disk 20 and this alsoaffects the performance of the hard disk drive.

Therefore, in order to ensure the reliability of the performance of ahard disk drive, vibrations generated during the operation of the harddisk drive need to be reduced. Further, since a personal computeremploying a hard disk drive must be compatible with relatively quietsurroundings, restraint of vibrations of a hard disk drive, andresultant reduction of noises are increasingly important problems to besolved.

SUMMARY OF THE INVENTION

To solve the above-described problems, it is an aspect of the presentinvention to provide a hard disk drive provided with a vibrationreducing damper for reducing noises by restraining vibrations generatedby a spindle motor from transferring to a cover plate of a housingthereof.

It is another aspect of the present invention to provide a hard diskdrive provided with a vibration-reducing damper for reducing vibrationsof disks by damping vibrations generated by a spindle motor.

Accordingly, to achieve the above aspects, there is provided a hard diskdrive including a housing having a base plate and a cover plate providedwith a through hole, a spindle motor including a shaft which issupported on the base plate and the upper end of which is joined to thecover plate by a screw inserted through the through hole, and a hubinstalled around the outer circumference of the shaft to be rotatable,at least one data storage disk which is joined to the outside of the hubto be rotated together with the hub, a head assembly for recording dataonto the disk and reading recorded data from the disk, and a damperwhich is interposed between the screw and the cover plate and includesat least one viscoelastic material layer.

In the present invention, the damper restrains vibrations generated bythe spindle motor from being transferred to the cover plate so as toreduce noises, and damps the vibrations so as to reduce fluttering ofthe disk.

The damper may be composed of a ring-shaped viscoelastic material layer.For example, the head portion of the screw and the through hole arepreferably, but not necessarily, tapered so that the diameters thereofbecome smaller toward the shaft. Further, the damper is preferably, butnot necessarily, tapered so as to closely contact the outercircumferential surface of the head portion of the screw and the innercircumferential surface of the through hole while interposedtherebetween.

Therefore, the damper can be installed easily to closely contact theinner circumferential surface of the through hole, and the shaft can befixed to the cover plate more strongly with the screw.

In addition, the damper is preferably, but not necessarily limited tobeing, formed by attaching a viscoelastic material layer having apredetermined thickness directly to the outer circumferential surface ofthe head portion of the screw.

Accordingly, since the damper is attached to the screw in advance,assembly thereof is simple, and the damper is prevented from escapingfrom its place.

Further, the damper preferably, but not necessarily, has a multi-layeredstructure in which at least one high stiffness layer having relativelyhigher stiffness and at least one low stiffness layer having relativelylower stiffness are alternately laminated.

In this example, but not by way of limitation, the damper may have adual-layered structure composed of a high stiffness layer and a lowstiffness layer, or a tri-layered structure composed of two highstiffness layers and one low stiffness layer interposed therebetween.

Preferably, but not necessarily, the damper has a multi-layeredstructure composed of a plurality of high stiffness layers and aplurality of low stiffness layers that are alternately laminated.

In addition, it is preferable, but not necessary, that the thickness ofthe low stiffness layer is thinner than the thickness of the highstiffness layer.

Further, it is preferable, but not necessary, that the high stiffnesslayer is made of a metal or plastic material, and the viscoelastic layerincludes rubber or resin.

According to a non-limiting example of the present invention, since thestiffness in radial directions is reduced to a relatively less extent,and the stiffness in an axial direction is reduced to a relatively moreextent in the damper, the rocking mode frequency can be kept to besufficiently high due to the damper while vibrations in an axialdirection generated by the spindle motor are restrained from beingtransferred to the cover plate due to the damper.

BRIEF DESCRIPTION OF THE DRAWINGS

The above aspects and advantages of the present invention will becomemore apparent by describing in detail illustrative, non-limitingembodiments thereof with reference to the attached drawings, in which:

FIG. 1 is a schematic exploded perspective view illustrating aconventional hard disk drive;

FIG. 2 is a vertical section view illustrating an assembly structure ofa housing and a spindle motor of the hard disk drive shown in FIG. 1;

FIG. 3 is a vertical section view illustrating an assembly structure ofa housing and a spindle motor of a hard disk drive provided with avibration reducing damper according to a first illustrative,non-limiting embodiment of the present invention;

FIG. 4 is a vertical section view illustrating an assembly structure ofa housing and a spindle motor of a hard disk drive provided with avibration reducing damper according to a second illustrative,non-limiting embodiment of the present invention;

FIG. 5 is a vertical section view illustrating an assembly structure ofa housing and a spindle motor of a hard disk drive provided with avibration reducing damper according to a third illustrative,non-limiting embodiment of the present invention;

FIG. 6 is a vertical section view illustrating an assembly structure ofa housing and a spindle motor of a hard disk drive provided with avibration reducing damper according to a fourth illustrative,non-limiting embodiment of the present invention;

FIGS. 7A and 7B are diagrams illustrating behaviors of a vibrationreducing damper having a multi-layer structure according to anillustrative, non-limiting embodiment of the present invention, FIG. 7Ashows a shape of the damper when no force is applied, and FIG. 7B showsa shape of the damper when a force is being applied;

FIG. 8 is a graph illustrating spectra of noises of the hard disk driveaccording to the second illustrative, non-limiting embodiment of thepresent invention shown in FIG. 4 and a conventional hard disk drive;and

FIGS. 9A and 9B are graphs illustrating rocking frequencies and diskfluttering of the hard disk drive according to the second illustrative,non-limiting embodiment of the present invention shown in FIG. 4 and aconventional hard disk drive, FIG. 9A shows rocking frequencies and diskfluttering of the conventional hard disk drive, and FIG. 9B showsrocking frequencies and disk fluttering of the hard disk drive accordingto the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

FIG. 3 is a vertical section view illustrating an assembly structure ofa housing and a spindle motor of a hard disk drive provided with avibration reducing damper according to a first embodiment of the presentinvention.

Referring to FIG. 3, a hard disk drive according to a firstillustrative, non-limiting embodiment of the present invention includesa housing 110 which composed of a base plate 111 and a cover plate 112,and a spindle motor 130, a magnetic disk unit 120, and a head assembly40 (please refer to FIG. 1) are installed in the housing 110.

The base plate 111 of the housing 110 supports the spindle motor 130 andthe head assembly, and the cover plate 112 is joined to the upper partof the base plate 111, and serves to envelop and protect the magneticunit 120 and the like. In addition, a through hole 113 is provided at apredetermined position of the cover plate 112 so that a screw 139 forjoining a shaft 132 of the spindle motor 130 to the cover plate 112 canpass through the through hole 113.

The spindle motor 130 is intended to rotate the magnetic disk unit 120,and is supported by a flange 131 which is fixedly installed on the baseplate 111. The lower end portion of the shaft 132 of the spindle motor130 is fixed to the flange 131, and the upper end portion thereof isfixed to the cover plate 112 by the screw 139. A hub 133 is rotatablyinstalled around the shaft 132 generally with bearings interposedtherebetween.

The magnetic disk unit 120 is a recording medium, and is fitted aroundthe outer circumference of the hub 133. The magnetic disk unit 120 maybe composed of one magnetic disk, or may be composed of two or moremagnetic disks to increase a recording capacity of data. When themagnetic disk unit 120 is composed of two or more magnetic disks, one ormore ring-shaped spacers 134 are installed around the outercircumference of the hub 133 to maintain a predetermined distancebetween the disks. In addition, a clamp 135 is joined to the upperportion of the hub 133 to prevent the magnetic disk unit 120 from beingseparated from the hub 133.

The head assembly is intended to read data from the magnetic disk unit120 or to write data to the magnetic disk unit 120, and is installed inthe housing 110 while being supported on the base plate 111.

In addition, a hard disk drive according to a first embodiment of thepresent invention includes, but is not limited to, a damper 150interposed between the screw 139 and the cover plate 112 as acharacteristic element of a non-limiting example of the presentinvention. The damper 150 is composed of one layer made of aviscoelastic material such as rubber or resin, and has a ring shape sothat the ring-shaped damper 150 can be inserted between the outercircumferential surface of the head portion 139 a of the screw 139 andthe inner circumferential surface of the through hole 113 of the coverplate 112, and contact the two surfaces closely.

As described above, in the hard disk drive according to the firstillustrative, non-limiting embodiment of the present invention, sincethe shaft 132 of the spindle motor 130 is not directly joined to thecover plate 112 by the screw 139, and the viscoelastic damper 150 isinterposed between the screw 139 and the cover plate 112, vibrationsgenerated by the spindle motor 130 are prevented from being transferredto the cover plate 112. That is, since the damper 150 damps vibrationstransferred from the spindle motor 130 to the housing 110, vibrations ofthe whole hard disk drive are reduced, and noises generated by thevibrations are reduced.

In addition, the damper 150 serves to damp vibrations of the spindlemotor 130, and therefore disk fluttering due to vibrations of thespindle motor 130 is reduced. This will be described in detail later.

As shown in FIG. 3, the damper 150 preferably, but not necessarily, hasa tapered ring shape. Accordingly, the head portion 139 a of the screw139 and the inner circumferential surface of the through hole 113 are,for example, but not by way of limitation, tapered to have smallerdiameters toward the shaft 132. Such a shape permits the damper 150 tobe inserted closely between the outer circumferential surface of thehead portion 139 a of the screw 139 and the inner circumferentialsurface of the through hole 113, and also permits the shaft 132 to befirmly fastened to cover plate 112 by the screw 139.

In addition, it is preferable, but not necessary, that the damper 150is, in advance, attached to the outer circumferential surface of thehead portion 139 a of the screw 139 with an adhesive. This permitsassembly operations to be performed more easily, and prevents the damper150 from being separated from its installed place due to vibrations.

FIGS. 4 through 6 show vertical section views of hard disk drivesaccording to other illustrative, non-limiting embodiments of the presentinvention having respective dampers composed of multiple layers. Here,the same reference numerals denote similar members of theabove-described first embodiment shown in FIG. 3.

First, referring to FIG. 4, a hard disk drive according to a secondillustrative, non-limiting embodiment of the present invention includes,but is not limited to, a damper 250 having a dual-layered structurecomposed of a high stiffness layer 251 and a low stiffness layer 252, asa characteristic element of the present invention. The high stiffnesslayer 251 is made of metal or plastic having relatively higherstiffness, and the lower stiffness layer 252 is made of viscoelasticmaterial such as rubber or resin having relatively lower stiffness. Thehigher stiffness layer 251 has a stepped portion formed on the innercircumferential surface thereof so that the head portion 239 a can beseated on the stepped portion. The lower surface of the higher stiffnesslayer 251 closely contacts the upper surface of a shaft 132. The highstiffness layer 251 acts as a busing for the head portion 239 a of ascrew 239. In addition, the low stiffness layer 252 is formed tosurround the outer circumferential surface of the high stiffness layer251, and the outer circumferential surface of the lower stiffness layer252 contact the inner circumferential surface of a cover plate 112.

With the above-described configuration, vibrations generated by aspindle motor 130 are not directly transferred to the cover plate 112,and are indirectly transferred to the cover plate 112 after being dampedby the low stiffness layer 252 of the damper 250 via the high stiffnesslayer 251. Accordingly, vibrations transferred to the cover plate 112are attenuated markedly, and noises due to vibrations are reduced. Also,disk fluttering can be reduced due to the damper 250 as in theabove-described first illustrative, non-limiting embodiment.

Though FIG. 4 shows, by example, but not by way of limitation, that thehigh stiffness layer 251 of the damper 250 contacts the screw 239, andthe low stiffness layer 252 contacts the inner circumferential surfaceof a through hole 113, to the contrary, the damper 250 may be configuredso that the low stiffness layer 252 of the damper 250 contacts the screw239, and the high stiffness layer 251 contacts the inner circumferentialsurface of the through hole 113.

Referring to FIG. 5, a hard disk drive according to a thirdillustrative, non-limiting embodiment of the present invention includes,but is not limited to, a damper 350 having a tri-layered structurecomposed of two high stiffness layers 351 a and 351 b and one lowstiffness layer 352. The high stiffness layers 351 a and 351 b are madeof metal or plastic having relatively higher stiffness, and the lowstiffness 352 is made of an viscoelastic material such as rubber orresin having relatively lower stiffness, as the above-described secondillustrative, non-limiting embodiment. The low stiffness layer 352 isinterposed between the two high stiffness layers 351 a and 351 b. Of thetwo high stiffness layers 351 a and 351 b, the inner high stiffnesslayer 351 a positioned at the inner side of the low stiffness layer 352contacts a screw 339, and the outer high stiffness layer 351 bpositioned at the outer side of the low stiffness layer 352 contacts theinner circumferential surface of a through hole 113 of a cover plate112. In addition, a stepped portion on which the head portion of thescrew 339 is seated is formed so that the inner high stiffness layer 351a can act as a bushing. The lower surface of the inner high stiffnesslayer 351 a closely contacts the upper surface of a shaft 132.

In addition, it is preferable, but not necessary, that the thickness ofthe low stiffness layer 352 is thinner than the thickness of the highstiffness layer 351 a and 351 b, and this is intended to form the damper350 in which the stiffness in radial directions is reduced to arelatively less extent, and the stiffness in an axial direction isreduced to a relatively more extent, as will be described in detaillater.

With the above damper 350, the rocking-mode frequency can be maintainedin a sufficiently high state while axial vibrations generated by aspindle motor 130 are restrained from being transferred to the coverplate 112. In addition, with the damper 350, transference of vibrationscan be restrained, and disk fluttering can be reduced.

Referring to FIG. 6, a hard disk drive according to a fourthillustrative, non-limiting embodiment of the present invention includes,but is not limited to, a damper 450 composed of multiple layers in whicha plurality of high stiffness layers 451 a, 451 b, 451 c, and 451 d anda plurality of low stiffness layers 452 a, 452 b, and 452 c arealternately laminated. Of the plurality of high stiffness layers, thehigh stiffness layer 451 a positioned at an innermost side contacts ascrew 439, and the high stiffness layer 451 d positioned at an outermostside contacts the inner circumferential surface of a through hole 113 ofa cover plate 112. In addition, a stepped portion on which the headportion 439 a of a screw 439 is seated is formed at the innercircumferential surface of the innermost high stiffness layer 451 a sothat the high stiffness layer 451 a can act as a bushing. The lowersurface of the high stiffness layer 451 a closely contacts the uppersurface of a shaft 132.

In addition, it is preferable, but not necessary, that the thickness ofthe low stiffness layers 452 a, 452 b, and 452 c is thinner than thethickness of the high stiffness layers 451 a, 451 b, 451 c, and 451 dsince axial vibrations generated by a spindle motor 130 can be preventedfrom being transferred to a cover plate 112 and the rocking-modefrequency can be maintained in a sufficiently high state.

This will be described in detail, for example, but not by way oflimitation, with reference to FIGS. 7A and 7B. In a damper having amulti-layered structure in which high stiffness layers having relativelythicker thickness and low stiffness layers having relatively thinnerthickness are alternately laminated, when a compressing force Fc in aradial direction of the damper and a shearing force Fs in the directionparallel to the bordering surfaces of the layers, i.e., in the radialdirection are applied to the damper as shown in FIG. 7A, in the damper,a strain Ss in the axial direction due to the shearing force is greaterthan a strain Sc in the radial direction due to the compressing force asshown in FIG. 7B. That is, in the damper configured as above, whereasthe stiffness in the axial direction is generally reduced due to the lowstiffness layers to a relatively greater extent, the stiffness in theradial direction is reduced to a relatively smaller extent.

Again, referring to FIG. 6, for example, but not by way of limitation,with the damper 450 having the above multi-layered structure, whileaxial vibrations generated by the spindle motor 130 are restrained frombeing transferred to the cover plate 112 due to the relatively lowstiffness in the axial direction, the rocking-mode frequency can bemaintained in a sufficiently high state due to the relatively highstiffness in the radial direction.

Next, noises, rocking-mode frequencies, and fluttering of a hard diskdrive according to an illustrative, non-limiting embodiment of thepresent invention will be described, for example, but not by way oflimitation, while being compared with those of a conventional hard diskdrive.

FIG. 8 shows, for example, but not by way of limitation, a graphillustrating spectra of noises of the hard disk drive according to thesecond illustrative, non-limiting embodiment of the present inventionshown in FIG. 4 and a conventional hard disk drive. Data shown in thegraph were measured at the upper portion of the hard disk drives.

As shown in FIG. 8, for example, but not by way of limitation, it can befound that noises, shown in gray solid lines, of the hard disk driveaccording to the present invention are generally reduced as comparedwith those, shown in black solid lines, of the conventional hard diskdrive.

The following Table 1 shows, for example, but not by way of limitation,noise values measured at the upper and lower portions of the hard diskdrive according to the present invention and those of the conventionalhard disk drive. TABLE 1 Position of Measurement HDD (Present Invention)HDD (Conventional) Upper Portion 20.8 dBA 21.2 dBA Lower Portion 21.5dBA 21.9 dBA

Referring to Table 1, it can found that noises of the hard disk driveaccording to the present invention were, for example, but not by way oflimitation, reduced by about 0.4 dBA at the upper and lower portionswhen compared with those of the conventional hard disk drive. Thus, inthe hard disk drive according to the illustrative, non-limitingembodiment of the present invention, since vibrations generated by thespindle motor are restrained from being transferred to the cover platedue to the damper interposed between the screw and the cover plate,vibrations of the whole hard disk drive are reduced, and accordinglynoises thereof are also reduced.

FIGS. 9A and 9B are graphs illustrating, for example, but not by way oflimitation, rocking frequencies and disk fluttering of the hard diskdrive according to the second illustrative, non-limiting embodiment ofthe present invention shown in FIG. 4 and a conventional hard diskdrive. Further, FIG. 9A shows, for example, but not by way oflimitation, rocking frequencies and disk fluttering of the conventionalhard disk drive. Moreover, FIG. 9B shows, for example, but not by way oflimitation, rocking frequencies and disk fluttering of the hard diskdrive according to the present invention.

Referring to FIGS. 9A and 9B, for example, but not by way of limitation,since a rocking frequency of the hard disk drive according to theillustrative, non-limiting embodiment of the present invention is about725 Hz, it can be found that the rocking frequency thereof was notsubstantially lowered as compared with a rocking frequency of 758 Hz ofthe conventional hard disk drive. This means that a sufficiently highrocking frequency can be maintained according to the illustrative,non-limiting embodiment of the present invention, and thereforeresonance phenomena do not occur, which occur when the rocking frequencymatches a vibration frequency of the spindle motor due to allowabletolerance, assembly tolerance, and the like of a ball bearing of thespindle motor, which exists in a relatively low frequency band, forexample, in the vicinity of 500 Hz.

In addition, since total fluttering of the hard disk drive according tothe illustrative, non-limiting embodiment of the present invention isabout 72 μm/s, it can be found that the total fluttering is markedlylowered when compared with total fluttering 90 μm/s of the conventionalhard disk drive. In particular, with the present invention, vibration atthe rocking frequency decreases markedly. The reason is that the damperinstalled at the upper portion of the spindle motor absorbs thevibration energy of the spindle motor, and damps disk fluttering.

As described above, for example, but not by way of limitation, with thehard disk drive provided with a vibration reducing damper according tothe illustrative, non-limiting embodiment of the present invention,since vibrations generated by the spindle motor are restrained frombeing transferred to the cover plate due to the damper while the rockingmode frequency is kept to be sufficiently high due to the damper, noisescan be reduced in the whole hard disk drive.

In addition, since the damper damps vibrations of the spindle motor toreduce disk fluttering, reliability of recording/reproduction of datato/from a disk can be enhanced.

While this invention has been particularly shown and described withreference to illustrative, non-limiting embodiments thereof, theillustrative embodiments are not meant to limit the present invention tothose implementations. Further, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims.

1. A hard disk drive comprising: a housing comprising a base plate and acover plate provided with a through hole; a spindle motor comprising ashaft which is supported on the base plate and the upper end of which isjoined to the cover plate by a screw inserted through the through hole,and a hub installed around the outer circumference of the shaft to berotatable; at least one data storage disk joined to the outside of thehub and capable of being rotated together with the hub; a head assemblyfor recording data onto the disk and reading recorded data from thedisk; a damper which is interposed between the screw and the coverplate, the damper comprising at least one viscoelastic material layer,wherein the head portion of the screw and the through hole are tapered,such that the diameters thereof become smaller toward the shaft, andwherein the damper is tapered, thereby contacting the outercircumferential surface of the head portion of the screw and the innercircumferential surface of the through hole while being interposedtherebetween.
 2. The hard disk drive of claim 1, wherein the damperrestrains vibrations generated by the spindle motor from beingtransferred to the cover plate, thereby reducing noises, and wherein thedamper damps the vibrations, thereby reducing fluttering of the disk. 3.The hard disk drive of claim 1, wherein the viscoelastic material layeris ring-shaped.